DE69106677T2 - Process for the preparation of orthophenylenediamine. - Google Patents

Description

The present invention relates to the preparation of ortho-phenylenediamine (sometimes referred to as OPDA) by the dehydrogenation of 1,2-diaminocyclohexane (sometimes referred to as DCH). The reaction can be represented as follows: Palladium catalyst cis- and trans - DCH

Background of the invention

OPDA is an intermediate in the production of fungicides. It can be produced by hydrogenation of ortho-nitroaniline.

DCH is produced as a byproduct during the hydrogenation of adiponitrile to hexamethylenediamine, a monomer used in the production of 6,6-nylon.

The object of the present invention is to provide a process for converting DCH into OPDA with high yields.

US-A 3 361 818 discloses the dehydrogenation of cyclohexylamine in the presence of a platinum-on-carbon catalyst which has been made alkaline with sodium hydroxide.

Summary of the invention

The present invention relates to a process for the preparation of o-phenylenediamine by dehydrogenation of 1,2- Diaminocyclohexane. The reaction takes place in the vapor phase at a pressure of 0.1 to 10 atmospheres and a temperature in the range of 175 to 225°C over a catalyst comprising a palladium metal and an alkali metal hydroxide dispersed on an inert substrate. The catalyst preferably contains between about 0.1 and 5 weight percent palladium metal and about 0.2 to 1.0 percent alkali metal hydroxide. Preferred inert substrates include alumina, silica, aluminum silicate, magnesium silicate, and activated carbon. Lithium hydroxide is the preferred alkali metal hydroxide contained in the catalyst.

Detailed description

The process according to the invention is preferably carried out at a temperature in the range of 200 to 225°C and a pressure of 1 atmosphere.

The catalyst used is a supported palladium catalyst containing an alkali metal hydroxide. The catalyst can be prepared by treating an inert substrate with an aqueous solution of an alkali metal hydroxide and a palladium salt such as palladium chloride or nitrate. The substrate can be impregnated with a single solution containing both components or with two different solutions each containing one of the components. After impregnation, the catalyst is dried, usually at a temperature in the range of about 70 to 200°C and preferably 100 to 120°C. After drying, the palladium salt is reduced to metallic palladium and the catalyst is ready for use. Alternatively, a commercially available catalyst of palladium metal on an inert substrate can be impregnated with alkali metal hydroxide solution and then dried.

The vaporous feed stream containing DCH may be diluted with such gases as nitrogen, hydrogen, ammonia, water vapor, carbon monoxide and methane. Nitrogen is a preferred diluent. The nitrogen serves to lower the partial pressure of DCH. If a diluent is used, it is usually added in an amount to ensure a molar ratio of diluent to DCH of about 1:1 to 20:1. Ammonia has the additional function of reducing deamination and preventing amine coupling.

The DCH used may be cis or trans and will most often be a mixture of cis and trans. If the DCH has been obtained as a by-product in the hydrogenation of adiponitrile, it will usually contain other impurities including 2-methylpentamethylenediamine. Typically, a stream of DCH from this source will contain 1 to 25 wt.% 2-methylpentamethylenediamine.

example 1

Forty cubic centimeters (33 g) of 5 x 8 mesh beads of 0.5% palladium metal on alumina (Calsicat Corp.) with a surface area of 90 m2/g were treated with 100 mL of an aqueous 3% LiOH solution for six hours at 25°C. The catalyst was filtered and washed twice with 100 mL of deionized water, followed by drying at 110°C for two hours. Acid titration of the starting solution and the mother liquor and washes resulted in a deposition of 0.61% LiOH on the catalyst.

About 40 ml of this catalyst was introduced into an oil-jacketed tubular glass reactor with a length of 50 cm and a diameter of 2.5 cm.

The tubular reactor loaded with the catalyst was heated with a high temperature fluid. The temperature of the circulating oil was 200ºC. The DCH was continuously fed into the reactor tube at 0.25 ml/min by means of a dosing pump. A 10 ml bed of glass beads was used at the top of the reactor to produce a gaseous To ensure material supply to the catalyst.

Nitrogen diluent was fed together with the vaporized DCH. The reacted effluent was cooled to 15ºC in two stages. Samples were taken from the condensed reaction product and their composition was determined by capillary gas chromatography. Based on these determinations and the weight of DCH fed to the reactor during seven hours, the conversion of DCH and the selectivity to OPDA were calculated.

The selectivities of OPDA as a function of temperature, LiOH loading and N2 diluent are summarized in the table below: Aromatization of 1,2-diaminocyclohexane to o-phenylenediamine %DCH Conversion %OPDA Yield (1) NH3 instead of N2 (2) 3% H2 added to N2 (3) KOH (4) Feedstock: 99% trans-DCH (5) 70/30 w/w DCH/water

Claims (4)

1. A process for the preparation of ortho-phenylenediamine which comprises dehydrogenating 1,2-diaminocyclohexane at a temperature of 175 to 225°C in the vapor phase at a pressure of 0.1 to 10 atmospheres over a catalyst containing a palladium metal and an alkali metal hydroxide dispersed on an inert substrate. 2. The process of claim 1, wherein the catalyst contains between 0.1 and 5 wt.% palladium and 0.2 to 1.0% alkali metal hydroxide. 3. The process of claim 2, wherein the inert substrate is selected from alumina, silicon oxide, aluminum silicate, magnesium silicate and activated carbon. 4. The process of claim 1, wherein the alkali metal hydroxide is lithium hydroxide.